JP6821322B2 - Image processing device and image processing method - Google Patents

Description

The present invention relates to an image processing apparatus and an image processing method.

The display element (pixel circuit) of the active matrix type organic EL display device includes an organic EL element and a thin film transistor (TFT). Then, by controlling the voltage applied to the display element, the current flowing through the organic EL element is controlled, and the emission brightness of the organic EL element is controlled.

FIG. 14 shows an example of the relationship between the voltage (input voltage) input to the display element and the emission brightness of the display element. FIG. 14 also shows the circuit of the display element. The emission brightness (emission amount) of the organic EL element is substantially proportional to the current flowing through the organic EL element. Therefore, the relationship between the input voltage and the emission brightness is similar to the VI characteristics of the TFT. Specifically, as shown in FIG. 14, the emission brightness of the display element rises from the vicinity of the threshold voltage Vth of the TFT.

Therefore, if the electrical characteristics of the TFT (threshold voltage Vth, etc.) vary among the display elements, the relationship between the input voltage and the emission brightness varies among the display elements, and the display image (image displayed on the screen) has uneven brightness. Variations in the characteristics of display elements, such as the electrical characteristics of TFTs, occur, for example, due to manufacturing problems in the display elements. Further, the characteristics of the display element change due to a change in the temperature around the display element, aged deterioration of the display element, and the like. Therefore, variations in the characteristics of the display element also occur due to changes in the temperature around the display element, aging deterioration of the display element, and the like.

A technique for reducing luminance unevenness is disclosed in, for example, Patent Document 1. In the technique disclosed in Patent Document 1, a plurality of correction values corresponding to a plurality of areas on the screen are prepared in advance, and the image data is corrected using the plurality of correction values.

However, when the characteristics (relationship between the input voltage and the emission luminance) are different between the display elements, the luminance unevenness may not be sufficiently reduced even if the technique disclosed in Patent Document 1 is used. In a self-luminous display device such as an organic EL display device, the characteristics often differ between the display elements. Therefore, in the self-luminous display device, even if the technique disclosed in Patent Document 1 is used, it is often not possible to sufficiently reduce the luminance unevenness.

Here, in an organic EL display device capable of expressing gradation of 10 bits (gradation value = 0 to 1023), the display brightness (screen brightness) of gradation value 1 is higher than that of other display elements. Consider a case where an element (high-luminance element) exists and each display element performs a display corresponding to a gradation value 1. In this case, the display brightness of the high-luminance element causes a brightness unevenness higher than the display brightness of the other display elements. In this case, even if the gradation value of the high-luminance element is corrected, the luminance unevenness cannot be reduced. When the gradation value of the high-luminance element is corrected so that the display brightness of the high-luminance element is lowered, a gradation value other than 0 cannot be selected as the corrected gradation value of the high-luminance element. When the gradation value of the high-luminance element is corrected to 0, the high-luminance element is turned off, and the display brightness of the high-luminance element is lower than the display brightness of other display elements.

Japanese Unexamined Patent Publication No. 2006-184305

An object of the present invention is to provide a technique capable of reducing brightness unevenness of a displayed image with high accuracy.

The first aspect of the present invention is
By the display unevenness of the display device by using the first correction value for correcting the input image data of the first number of bits to low reduction, first correction means for generating a first corrected image data of the first number of bits When,
Based on a predetermined first correction value that can be used by the first correction means, the display unevenness is reduced with a higher resolution than that of the first correction means, and a gradation value that cannot be expressed by the first correction image data. The first corrected image data of the first bit number is the first bit number so that the display corresponding to the specific gradation value is realized by the display element of the display device and the display element around the display element. Corrected to the first corrected image data with a larger number of second bits than
In the first corrected image data of the second bit number, the conversion process of converting the number of bits from the second bit number to the first bit number and the error of the gradation value due to the conversion process are added to the surrounding pixels. By applying the error reduction processing to reduce by using
Second correction means for generating the second correction image data and
It is an image processing apparatus characterized by having.

A second aspect of the present invention is
By the display unevenness of the display device by using the first correction value for correcting the input image data of the first number of bits to low reduction, the first correction step of generating a first corrected image data of the first number of bits When,
Based on a predetermined first correction value that can be used in the first correction step, the display unevenness is reduced with a higher resolution than that of the first correction step, and a gradation value that cannot be expressed by the first correction image data. The first corrected image data of the first bit number is the first bit number so that the display corresponding to the specific gradation value is realized by the display element of the display device and the display element around the display element. Corrected to the first corrected image data with a larger number of second bits than
In the first corrected image data of the second bit number, the conversion process of converting the number of bits from the second bit number to the first bit number and the error of the gradation value due to the conversion process are added to the surrounding pixels. By applying the error reduction processing to reduce by using
The second correction step for generating the second correction image data and
It is an image processing method characterized by having.

A third aspect of the present invention is a program for causing a computer to execute each step of the above-mentioned image processing method.

According to the present invention, it is possible to reduce the brightness unevenness of the displayed image with high accuracy.

The figure which shows the configuration example of the system which concerns on Example 1. Block diagram showing a configuration example of the image display device according to the first embodiment The figure which shows an example of 1DLUT which concerns on Example 1. The figure which shows an example of the display image which concerns on Example 1. The figure which shows an example of 2DLUT which concerns on Example 1. A flowchart showing an example of the processing flow of the bit conversion unit according to the first embodiment. The figure which shows an example of the 1st correction image data which concerns on Example 1. The figure which shows an example of the 3rd correction image data which concerns on Example 1. The figure which shows an example of the dither matrix which concerns on Example 1. The figure which shows the specific example of the processing of the dither processing part which concerns on Example 1. Block diagram showing a configuration example of the image display device according to the second embodiment Block diagram showing a configuration example of the image display device according to the third embodiment The figure which shows the specific example of the processing of the error diffusion processing part which concerns on Example 3. The figure which shows an example of the display characteristic of a display element

<Example 1>
Hereinafter, Example 1 of the present invention will be described. In the following, an example in which the image processing device according to the present embodiment is provided in the image display device will be described, but the image processing device may be a device separate from the image display device. FIG. 1 is a diagram showing a configuration example of a system according to this embodiment. The system according to this embodiment includes an image display device 100 and an image output device 200. The image output device 200 is connected to the image display device 100 by using an SDI (Serial Digital Interface) cable. The method of connecting the image display device 100 and the image output device 200 is not particularly limited. The image display device 100 and the image output device 200 may be connected to each other by using a cable different from the SDI cable. The image display device 100 and the image output device 200 may be wirelessly connected to each other so that wireless communication can be performed between the image display device 100 and the image output device 200.

The image output device 200 outputs the image data OU_SIG to the image display device 100. In this embodiment, the image output device 200 outputs the image data OU_SIG to the image display device 100 via the SDI cable. In this embodiment, the image data OU_SIG is uncompressed image data. As the image output device 200, a personal computer, a storage device, or the like can be used. As a storage medium for storing the image data OU_SIG, a magnetic disk, an optical disk, a semiconductor memory, or the like can be used. The image data OU_SIG is not particularly limited. The image data OU_SIG may be compressed image data.

The image display device 100 performs image processing on the input image data (image data input to the image display device 100), and displays an image based on the image data after the image processing on the screen. In this embodiment, the image data OU_SIG output from the image output device 200 is input to the image display device 100. As the image display device 100, an organic EL display device, a liquid crystal display device, a plasma display device, or the like can be used. When the image processing device according to the present embodiment is a device separate from the image display device 100, a personal computer or the like can be used as the image processing device.

FIG. 2 is a block diagram showing a configuration example of the image display device 100. The image display device 100 includes an input unit 101, a LUT storage unit 102, a first correction unit 103, a second correction unit 107, and a display unit 106.

The input unit 101 acquires the input image data. In this embodiment, the input unit 101 is composed of SDI communication standard terminals and their processing circuits. The input unit 101 generates image data IM_DATA by performing bit conversion processing, format conversion processing, and the like on the image data OU_SIG input to the input unit 101. Then, the input unit 101 outputs the image data IM_DATA to the first correction unit 103. The "image data OU_SIG" can be called "input image data", and the "image data IM_DATA" can be called "input image data".

In this embodiment, when the 12-bit image data OU_SIG is input to the input unit 101, the input unit 101 performs a bit conversion process for converting the number of bits of the image data from 12 bits to 10 bits. Further, when the image data OU_SIG in the YCbCr format is input to the input unit 101, the input unit 101 performs a format conversion process for converting the data format of the image data from the YCbCr format to the RGB format. In this embodiment, for the sake of simplicity, processing for any one of the R value, the G value, and the B value will be described.

The number of bits of the image data OU_SIG input to the input unit 101 may be more or less than 12 bits. The data format of the image data OU_SIG is not limited to the YCbCr format. The number of bits of the image data IM_DATA output from the input unit 101 may be more or less than 10 bits. The data format of the image data IM_DATA is not limited to the RGB format. Further, when the image data OU_SIG has a desired number of bits and a desired data format, the bit conversion process, the format conversion process, and the like may be omitted. Then, the input unit 101 may output the same image data IM_DATA as the image data OU_SIG to the first correction unit 103.

The LUT storage unit 102 is a storage unit that stores a correction value (first correction value) based on the display characteristics of the image display device 100. The first correction value is a correction value that reduces display unevenness due to variations in display characteristics among display elements. The display unevenness includes at least one of the luminance unevenness which is the unevenness of the display luminance (screen brightness) and the color unevenness which is the unevenness of the display color (screen color). As the LUT storage unit 102, a magnetic disk, an optical disk, a semiconductor memory, or the like can be used.

In this embodiment, the LUT storage unit 102 stores 1DLUT (one-dimensional look-up table; first input / output information) using the gradation value of the image data IM_DATA as the input value and the first correction value as the output value. To do. The LUT storage unit 102 stores a plurality of 1D LUTs corresponding to the plurality of display elements included in the display unit 106. For example, when the display unit 106 has a total of 230,400 display elements of 1920 in the horizontal direction and 1200 in the vertical direction, the LUT storage unit 102 stores 230,400 1DLUTs corresponding to the 230,400 display elements, respectively. .. In this embodiment, 1DLUT has 5 grid points. Each grid point is associated with a gradation value that can be taken by the image data IM_DATA and a first correction value that corrects the gradation value. The first correction value corresponding to the gradation value is, for example, a correction value that brings the brightness (display brightness) of the display element closer to the reference brightness (ideal brightness) corresponding to the gradation value. The reference brightness can also be said to be "ideal brightness of the display element".

The LUT storage unit 102 may be a storage device built in the image display device 100 (image processing device according to this embodiment), or may be used in the image display device 100 (image processing device according to this embodiment). On the other hand, it may be a removable storage device. Further, the number of grid points of 1DLUT may be more than or less than five. Further, a function may be used as the first input / output information. Further, a plurality of display element groups including two or more display elements may be set. Then, a plurality of first input / output information corresponding to each of the plurality of display element groups may be prepared. That is, the first input / output information may be shared between two or more display elements included in the display element group.

FIG. 3 is a schematic view showing an example of 1DLUT. The 1DLUT of FIG. 3 has five grid points corresponding to five gradation values 0, 8, 24, 64, and 128 among a plurality of 10-bit gradation values. The first correction value data0 is used for the grid points corresponding to the gradation value 0, the first correction value data8 is used for the grid points corresponding to the gradation value 8, and the first correction is made for the grid points corresponding to the gradation value 24. The value data24 is associated. The first correction value data64 is stored in the grid points corresponding to the gradation value 64, and the first correction value data128 is stored in the grid points corresponding to the gradation value 128. In this embodiment, the first correction value is an integer of -4 or more and +4 or less. Further, in this embodiment, the display element has a thin film transistor (TFT). For example, the image display device 100 is an organic EL display device. The minimum values (gradation value 8) of the four gradation values 8, 24, 64, and 128, which are different from the gradation value 0, correspond to the threshold voltage of the reference (ideal) TFT.

The possible value of the first correction value may be narrower or wider than the range of -4 or more and +4 or less. Further, the number of grid points may be more or less than five. Further, the gradation values corresponding to the grid points are not limited to the gradation values 0, 8, 24, 64, 128. Further, the minimum gradation value different from the gradation value 0 may be larger or smaller than the gradation value corresponding to the threshold voltage of the reference TFT.

When displaying image data with uniform gradation values, it is desirable that the brightness of each display element is controlled to the same brightness. However, when the display characteristics vary among the display elements (when there are individual differences in the display characteristics), the brightness may vary between the display elements. That is, uneven brightness may occur. When the display unit 106 has a plurality of display elements for each of the plurality of colors, the variation in the display characteristics among the display elements corresponding to a certain color is the display characteristics among the display elements corresponding to the other colors. May differ from variability. In that case, a luminance distribution different from the luminance distribution corresponding to another color may be obtained as the luminance distribution (display luminance distribution) corresponding to a certain color. If the brightness distribution differs between colors, color unevenness occurs.

FIG. 4 shows an example of a display image (image displayed on the screen) when each display element displays according to the gradation value 8. In FIG. 4, the screen area A is a part of the screen and is composed of four display elements A1 to A4. The screen area B is a part of the screen and is composed of four display elements B1 to B4. Here, it is assumed that the reference brightness corresponding to the gradation value 8 is 0.0025 [cd / m ² ].

It is not necessary to correct the gradation corresponding to the display element whose brightness is equal to the reference brightness. In FIG. 4, the brightness of the display elements A1 to A4 are all 0.0025 [cd / m ² ]. Therefore, it is not necessary to correct the gradation value corresponding to the display elements A1 to A4. On the other hand, when there is a partial region consisting of a plurality of display elements whose brightness is higher than the reference brightness, when there is a partial region consisting of a plurality of display elements whose brightness is lower than the reference brightness, etc. Luminance unevenness occurs in those partial regions. In FIG. 4, the brightness of the display element B1 is 0.010 [cd / m ² ], the brightness of the display elements B2 and B3 is 0.0075 [cd / m ² ], and the brightness of the display element B4 is 0. It is 0050 [cd / m ² ]. That is, the brightness of the display elements B1 to B4 is higher than the reference brightness, and the brightness varies among the display elements B1 to B4. Therefore, uneven brightness occurs in the screen area B. Therefore, in this embodiment, a correction value that brings the brightness of the display element closer to the reference brightness is prepared as the first correction value corresponding to the display element. Specifically, as the first correction value corresponding to the display element whose brightness is higher than the reference brightness, a correction value for reducing the brightness of the display element is prepared, and the first correction corresponding to the display element whose brightness is lower than the reference brightness is prepared. As a value, a correction value for increasing the brightness of the display element is prepared. More specifically, a negative correction value is prepared as the first correction value corresponding to the display element whose brightness is higher than the reference brightness, and the positive correction value is prepared as the first correction value corresponding to the display element whose brightness is lower than the reference brightness. Prepare a correction value.

The first correction unit 103 acquires the image data IM_DATA from the input unit 101, and acquires 1DLUT from the LUT storage unit 102. Then, the first correction unit 103 corrects the acquired image data IM_DATA using the acquired 1DLUT (first correction value). As a result, image data (first corrected image data) PC_DATA is generated. The first correction unit 103 outputs the generated image data PC_DATA to the second correction unit 107.

In this embodiment, for the sake of simplicity, an example in which the pixels of the image data IM_DATA and the display element have a one-to-one correspondence will be described. Therefore, the "1DLUT corresponding to the display element" can be said to be the "1DLUT corresponding to the pixel". In this embodiment, the gradation value of the pixel is corrected for each pixel by using the 1DLUT corresponding to the pixel. Specifically, the first correction value is acquired from the grid points corresponding to the gradation value of the image data IM_DATA among the plurality of grid points of 1DLUT. There may be no grid points corresponding to the gradation value of the image data IM_DATA. In that case, the first correction value corresponding to the gradation value of the image data IM_DATA is obtained by interpolation (linear interpolation, etc.) using a plurality of lattice points corresponding to the gradation value close to the gradation value of the image data IM_DATA. To be acquired. Then, the gradation value of the image data IM_DATA is corrected by using the acquired first correction value.

In this embodiment, the gradation value of the image data IM_DATA is calculated using the following formula 1. In Equation 1, "PC_DATA (x, y)" is the gradation value of the pixel of coordinates (horizontal position, vertical position) = (x, y) among the plurality of gradation values of the image data PC_DATA. "IM
"_DATA (x, y)" is the gradation value of the pixel of the coordinate (x, y) among the plurality of gradation values of the image data IM_DATA. “CValue (x, y)” is the first correction value obtained according to the gradation value IM_DATA (x, y).

PC_DATA (x, y) = IM_DATA (x, y) + cValue (x, y)
... (Equation 1)

The correspondence between the pixels and the display element is not particularly limited. A plurality of display elements may correspond to one pixel. In that case, for example, the representative values (maximum value, minimum value, average value, intermediate value, mode, etc.) of the plurality of first correction values corresponding to the plurality of display elements correspond to one pixel. It is used as the first correction value. One display element may correspond to a plurality of pixels. In that case, for example, the first correction value corresponding to one display element is used as the first correction value corresponding to each of the plurality of pixels. Further, the first correction value is not limited to the offset value to be added to the gradation value. As the first correction value, a gain value to be multiplied by the gradation value may be used.

The second correction unit 107 realizes a display corresponding to a specific gradation value by the display element and the display elements around the display element based on a predetermined first correction value that can be used by the first correction unit 103. As described above, the image data PC_DATA is corrected. As a result, image data (second corrected image data) OU_DATA is generated. The second correction unit 107 outputs the generated image data OU_DATA to the display unit 106. The specific gradation value is a gradation value according to the display characteristic (for example, a gradation value that should be obtained in consideration of the display characteristic), and is a gradation value that cannot be obtained by the image data PC_DATA. The predetermined first correction value is not particularly limited, but in this embodiment, an example in which the first correction value data8 for correcting the gradation value corresponding to the threshold voltage of the reference TFT is used as the predetermined first correction value. explain. The image data OU_DATA may be recorded in the storage unit without being output to the display unit 106.

The second correction unit 107 will be described in detail. As shown in FIG. 2, in this embodiment, the second correction unit 107 has a bit conversion unit 104 and a dither processing unit 105.

The bit conversion unit 104 acquires 2DLUT (two-dimensional look-up table; second input / output information). The 2DLUT uses a combination of the gradation value of the image data PC_DATA and the predetermined first correction value data8 as an input value. Then, the 2DLUT outputs a second correction value for correcting the gradation value of the image data PC_DATA, or a gradation value obtained by correcting the gradation value of the image data PC_DATA using the second correction value. And. For example, 2DLUT is recorded in advance in the LUT storage unit 102, and 2DLUT is acquired from the LUT storage unit 102. In this embodiment, the image data PC_DATA is corrected based on the acquired 2DLUT. A function may be used as the second input / output information.

The bit conversion unit 104 converts the number of bits of the image data PC_DATA from the number of first bits (10 bits) to the number of second bits, which is larger than the number of first bits, based on the predetermined first correction value data8. As a result, image data (third corrected image data) LC_DATA is generated. Specifically, the bit conversion unit 104 generates the image data LC_DATA by correcting the image data PC_DATA based on 2DLUT. The image data LC_DATA is, for example, image data having gradation values according to display characteristics. The bit conversion unit 104 outputs the generated image data LC_DATA to the dither processing unit 105. The number of second bits is not particularly limited, but in this embodiment, an example in which the number of second bits is 12 bits will be described.

FIG. 5 is a schematic view showing an example of 2DLUT. The 2DLUT in FIG. 5 uses a combination of the gradation value (10 bits) of the image data PC_DATA and the predetermined first correction value data8 as an input value. The 2DLUT in FIG. 5 uses the gradation value (12 bits) of the image data LC_DATA as the output value.

FIG. 6 is a flowchart showing an example of the processing flow of the bit conversion unit 104. The bit conversion unit 104 repeats the processes of S101 to S107 of FIG. 6 for all the pixels of the image data PC_DATA.

First, in S101, the bit conversion unit 104 acquires PC_LUT (x, y), which is a 1D LUT corresponding to the pixel of the coordinate (x, y), from the LUT storage unit 102. Next, in S102, the bit conversion unit 104 sets the gradation value PC_DATA (x, y), which is the gradation value of the pixel (x, y) of the image data PC_DATA, as the input gradation value pValue. Then, in S103, the bit conversion unit 104 sets PC_LUT (x, y, data8) as the input correction value cValue. PC_LUT (x, y, data8) is the first correction value indicated by PC_LUT (x, y), and is the first correction value data8 corresponding to the gradation value 8.

Next, in S104, the bit conversion unit 104 determines whether or not the combination of the input gradation value pValue and the input correction value cValue is used as the input value of the 2DLUT. When the combination of the input gradation value pValue and the input correction value cValue is used as the input value of the 2DLUT, the process proceeds to S105. If the combination of the input gradation value pValue and the input correction value cValue is not used as the input value of the 2DLUT, the process proceeds to S106.

In S105, the bit conversion unit 104 sets the output value 2DLUT (pValue, cValue) (12-bit gradation value) corresponding to the combination of the input gradation value pValue and the input correction value cValue as a temporary gradation value outputTmp. Obtained from 2DLUT. In S106, the bit conversion unit 104 generates a temporary gradation value outputTmp by converting the number of bits of the input gradation value pValue from 10 bits to 12 bits. In S106, the brightness corresponding to the gradation value is not converted. Specifically, in S106, 0 is added as the lower 2 bits to the input gradation value pValue. Then, in S107, the bit conversion unit 104 uses the temporary gradation value outputTmp obtained by the processing of S105 or S106 as the gradation value LC_DATA (x) which is the gradation value of the pixels (x, y) of the image data LC_DATA. , Y).

As the output value of 2DLUT, a correction value (second correction value) for correcting the gradation value of the image data PC_DATA to the gradation value of the image data LC_DATA may be used. In that case, a second correction value may be acquired from 2DLUT, and the gradation value of the image data PC_DATA may be corrected to the gradation value of the image data LC_DATA using the acquired second correction value. Further, as the output value of the 2DLUT, a gradation value of the image data OU_DATA, a correction value (second correction value) for correcting the gradation value of the image data PC_DATA to the gradation value of the image data OU_DATA, and the like may be used. .. In that case, conversion of the number of bits from the first bit to the second bit, processing by the dither processing unit 105, and the like become unnecessary.

In an image display device such as an organic EL display device, the display characteristics are often not good in a low gradation range, which is a range of low gradation values. In particular, the display characteristics are often not good in the gradation range in which the gradation value is less than 0.1% of the number of gradations (the number of gradation values that the image data can take). “The display characteristic is not good” means, for example, that “the display characteristic is significantly different from the reference characteristic (display characteristic corresponding to the reference TFT, etc.)”. For example, when the number of bits of the image data is 10 bits, the number of gradations is 1024. Therefore, the display characteristics are often not good in the gradation range where the gradation value is less than 1.024 (= 1024 × 0.001). That is, in the gradation range where the gradation value is 1 or less, the display characteristics are often not good.

Therefore, in the 2DLUT of FIG. 5, only the input gradation value pValue = 1 is set as the input value. In 2DLUT, another gradation value different from the gradation value 1 may be used as an input value. By increasing the number of gradation values used as the input value of the 2DLUT, the accuracy of the correction using the 2DLUT (correction based on the predetermined first correction value data8) can be improved.

Further, in this embodiment, the pixel corresponding to the display element whose brightness corresponding to the gradation value has a display characteristic higher than the reference brightness is targeted for correction. Therefore, in the 2DLUT of FIG. 5, only the input correction value cValue = negative value (-1 to -4) is set as the input value. "Input correction value cValue = negative value" means "corresponding to a display element having a display characteristic in which the brightness corresponding to the gradation value is higher than the reference brightness". Further, "input correction value cValue = negative value" is "correction for lowering the gradation value is required" and "displayed at a brightness higher than the reference brightness when the image data PC_DATA is not corrected". , Etc. also mean. Further, in the 2DLUT of FIG. 5, when the input gradation value is constant, the smaller the first correction value, which is a negative value, the smaller the value is used as the output value (gradation value of image data LC_DATA). .. This is because, in the display characteristics of the display element, the brightness (relative value with respect to the reference brightness) corresponding to the gradation value is higher as the first correction value, which is a negative value, is smaller.

Therefore, in this embodiment, only the gradation values of the pixels satisfying both the following conditions 1 and 2 are corrected based on the predetermined first correction value data8. It should be noted that only one of the conditions 1 and 2 may be considered, or the conditions 1 and 2 may not be considered. Other conditions may be considered.

Condition 1: Corresponds to a display element having a display characteristic in which the brightness corresponding to the gradation value is higher than the reference brightness.
Condition 2: The gradation value of the image data PC_DATA is less than 0.1% of the number of possible gradation values of the image data PC_DATA.

FIG. 7 shows the image data PC_DATA corresponding to the screen area B of FIG. 4 (the area including the four display elements B1 to B4). As shown in FIG. 7, the gradation value of the image data PC_DATA is 1 in all of the four display elements B1 to B4. The first correction value data8 of the display element B1 is -4, the first correction value data8 of the display element B2 is -3, the first correction value data8 of the display element B3 is -3, and the display element B4. The first correction value data8 of is -2. Here, the first correction value data8 varies among the four display elements B1 to B4 because the display characteristics vary among the four display elements B1 to B4. As described above, in the display characteristics of the display element, the brightness (relative value with respect to the reference brightness) corresponding to the gradation value is higher as the first correction value, which is a negative value, is smaller. Therefore, when the same gradation value is assigned to the four display elements B1 to B4, the display brightness varies among the four display elements B1 to B4.

FIG. 8 shows the image data LC_DATA corresponding to the screen area B of FIG. Specifically, FIG. 8 shows the gradation value obtained by correcting the gradation value of FIG. 7 using the 2DLUT of FIG. Regarding the display element B1, since the gradation value before correction is 1 (10 bits) and the first correction value data8 is -4, 1 (12 bits) can be obtained as the gradation value after correction. .. Regarding the display element B2, since the gradation value before correction is 1 (10 bits) and the first correction value data8 is -3, 2 (12 bits) can be obtained as the gradation value after correction. .. Regarding the display element B3, since the gradation value before correction is 1 (10 bits) and the first correction value data8 is -3, 2 (12 bits) is obtained as the gradation value after correction. .. As for the display element B4, since the gradation value before correction is 1 (10 bits) and the first correction value data8 is -2, 3 (12 bits) is set as the gradation value after correction. can get.

As shown in FIG. 8, the gradation value of the image data LC_DATA is less than 4 in all of the four display elements B1 to B4. That is, in all of the four display elements B1 to B4, the gradation value of the image data LC_DATA is less than the gradation value 1 of 10 bits. This means that the corrected gradation value corresponds to the brightness lower than the brightness corresponding to the gradation value before the correction. In this embodiment, the image data LC_DATA has a gradation value according to the display characteristics. Therefore, the fact that the gradation value of the image data LC_DATA is less than the gradation value 1 of 10 bits means that when the gradation value 1 of 10 bits is assigned to the display element, the display is performed with a brightness higher than the reference brightness. Means to be

The dither processing unit 105 uses the surrounding pixels to perform a conversion process for converting the number of bits from the second bit number (12 bits) to the first bit number (10 bits) and an error in the gradation value due to the conversion process. The image data LC_DATA is subjected to the error reduction processing for reduction. As a result, image data OU_DATA is generated. The dither processing unit 105 outputs the generated image data OU_DATA to the display unit 106.

In this embodiment, the dither processing unit 105 generates image data (fourth corrected image data) LC_DATA_DITH by applying an error reduction process, which is a filter process using a predetermined filter, to the image data LC_DATA. The above "filter processing" is called "dither processing", and the "predetermined filter" is called "dither matrix". The size of the dither matrix is not particularly limited, but in this embodiment, an example in which a dither matrix that refers to a total of 4 pixels of 2 pixels in the horizontal direction and 2 pixels in the vertical direction will be described. In this embodiment, dither processing is performed for each of a plurality of pixel groups (a pixel group consisting of a total of 4 pixels of 2 pixels in the horizontal direction and 2 pixels in the vertical direction). As a result, the entire image is dithered.

In the dither processing of this embodiment, the gradation value of the image data LC_DATA_DITH is calculated for each of the four pixels referred to in the dither matrix by using the following formula 2. In Equation 2, "LC_DATA_DITH (x, y)" is the gradation value of the pixel of the coordinate (x, y) among the plurality of gradation values of the image data LC_DATA_DITH. “LC_DATA (x, y)” is the gradation value of the pixel of the coordinate (x, y) among the plurality of gradation values of the image data LC_DATA. Then, "withMtx (x, y)" is an element corresponding to a pixel of coordinates (x, y) among a plurality of elements (correction values) of the dither matrix. The element of the dither matrix is not limited to the offset value to be added to the gradation value. As an element, a gain value to be multiplied by a gradation value may be used.

LC_DATA_DITH (x, y)
= LC_DATA (x, y) + withMtx (x, y)
... (Equation 2)

Then, the dither processing unit 105 generates the image data OU_DATA by performing the conversion process on the image data LC_DATA_DITH. In this embodiment, as the conversion process, a process of converting the number of bits from the number of second bits to the number of first bits is performed by truncating the bits (lower two bits). The conversion process is not limited to this. As the conversion process, a process of converting the number of bits from the number of second bits to the number of first bits by rounding up the number of bits, a process of converting the number of bits from the number of second bits to the number of first bits by rounding off the bits, and the like are performed. You may.

FIG. 9 shows an example of the dither matrix. In the dither matrix of FIG. 9, the element withMtx11 in the first row and the first column is 2, the element in the first row and the second column is 1, and the element in the second row and the first column is 0, and the element in the second row and the first column is 0. The eye element withMtx22 is 1. The number of bits of each element is 12 bits (the number of second bits).

FIG. 10 is a schematic view showing a specific example of the processing of the dither processing unit 105. FIG. 10 shows a process corresponding to the screen area B of FIG. In FIG. 10, the same image data LC_DATA as the image data LC_DATA shown in FIG. 8 is used. Further, in FIG. 10, the same dither matrix as the dither matrix shown in FIG. 9 is used.

The gradation value LC_DATA (1,1) in the first row and the first column is 1, and the element withMtx (1,1) in the first row and the first column is 2. Therefore, in FIG. 10, 3 (= 1 + 2) is obtained as the gradation value LC_DATA_DITH (1,1) in the first row and the first column. The gradation value LC_DATA (2,1) in the first row and second column is 2, and the element withMtx (2,1) in the first row and second column is 1. Therefore, in FIG. 10, 3 (= 2 + 1) is obtained as the gradation value LC_DATA_DITH (2,1) in the first row and the second column. The gradation value LC_DATA (1,2) in the second row and the first column is 2, and the element withMtx (1,2) in the second row and the first column is 0. Therefore, in FIG. 10, 2 (= 2 + 0) is obtained as the gradation value LC_DATA_DITH (1, 2) in the second row and the first column. The gradation value LC_DATA (2,2) in the second row and second column is 3, and the element dithMtx (2,2) in the second row and second column is 3. Therefore, in FIG. 10, 6 (= 2 + 2) is obtained as the gradation value LC_DATA_DITH (2, 2) in the second row and the second column.

Then, by truncating the lower 2 bits of the gradation values 3, 3, 2, 6 of the image data LC_DATA_DITH, the gradation values 0,0,0,1 of the image data OU_DATA can be obtained.

Here, as shown in FIG. 7, the gradation value of the image data PC_DATA is 1 in all of the four display elements B1 to B4. Then, in this embodiment, as shown in FIG. 10, the gradation value 1 of the image data PC_DATA is reduced to the gradation value 0 of the image data OU_DATA in the three display elements B1, B2, and B4. As a result, the display brightness of the screen area B can be reduced to a brightness lower than the brightness when the image data PC_DATA is not corrected. Further, for the display element B3, 1 is used as the gradation value of the image data OU_DATA. Therefore, the display brightness at the positions of the display elements B1, B2, and B4 is suppressed too low by the light from the display element B3. As a result, the display brightness in the screen area B can be brought close to the reference brightness, and the brightness unevenness in the screen area B can be reduced. Then, by performing the above-described processing on the entire screen, it is possible to reduce the uneven brightness of the entire screen. Further, when the display unit 106 has a plurality of display elements for each of the plurality of colors, the color unevenness can be reduced by performing the above processing for reducing the luminance unevenness for each of the plurality of colors.

The display unit 106 displays according to the image data OU_DATA. As the display unit 106, an organic EL display panel, a liquid crystal display panel, a plasma display panel, or the like can be used. The display unit 106 supplies, for example, a current corresponding to each gradation value of the image data OU_DATA to each display element. As a result, the display is performed according to the image data OU_DATA.

As described above, according to the present embodiment, the image data is corrected so that the display corresponding to the specific gradation value is realized by the display element and the display elements around it. As a result, the uneven brightness of the displayed image can be reduced with high accuracy.

<Example 2>
Hereinafter, Example 2 of the present invention will be described. In Example 1, an example of applying dither processing to the entire image has been described. In this embodiment, an example of limiting the image area to be subjected to dither processing will be described. In the following, a configuration and processing different from those of the first embodiment will be described, and a description of the same configuration and processing as that of the first embodiment will be omitted. FIG. 11 is a block diagram showing a configuration example of the image display device 300 according to the present embodiment. In FIG. 11, the same functional units as those in FIG. 2 (Example 1) are designated by the same reference numerals as those in FIG.

Similar to the dither processing unit 105 of the first embodiment, the dither processing unit 305 generates the image data OU_DATA by performing the dither processing and the conversion processing on the image data LC_DATA. However, in this embodiment, the dither processing unit 305 performs dither processing that refers to the plurality of pixels only when each of the plurality of pixels satisfies a predetermined condition. Also in this embodiment, a total of 4 pixels of 2 pixels in the horizontal direction and 2 pixels in the vertical direction are referred to in one dither processing. Therefore, in this embodiment, for each of the plurality of pixel groups, it is determined whether or not each of the four pixels included in the pixel group satisfies a predetermined condition. Then, dither processing is performed only on a pixel group composed of four pixels satisfying a predetermined condition.

The predetermined conditions are not particularly limited. However, from the viewpoint of reducing the luminance unevenness, the predetermined condition is preferably a condition that causes the luminance unevenness. For example, the predetermined condition preferably includes at least one of the condition 1 and the condition 2 described in the first embodiment. In this embodiment, an example in which the condition 1 described in the first embodiment is used as a predetermined condition will be described.

In this embodiment, the dither processing unit 305 acquires 1DLUT from the LUT storage unit 102, and for each of the four pixels included in the pixel group, whether or not the first correction value corresponding to that pixel is a negative value. To judge. Then, the dither processing unit 305 performs dither processing on the pixel group in which the first correction value of all four pixels is a negative value. On the other hand, the dither processing unit 305 omits the dither processing for the pixel group including the pixels whose first correction value is not a negative value, and adopts the gradation value of the image data LC_DATA as the gradation value of the image data LC_DATA_DITH. As described above, in this embodiment, only the pixel group in which the first correction value of all four pixels is a negative value is selected (determined) as the target of the dither processing.

As described above, according to the present embodiment, the dither processing for referring to the plurality of pixels is performed only when each of the plurality of pixels satisfies a predetermined condition. As a result, not only the brightness unevenness of the displayed image can be reduced with high accuracy, but also the processing load of the image processing apparatus can be reduced.

<Example 3>
Hereinafter, Example 3 of the present invention will be described. In Examples 1 and 2, an example in which dither processing is performed as error reduction processing has been described. In this embodiment, an example in which an error reduction process different from the dither process is performed will be described. In the following, a configuration and processing different from those of the first embodiment will be described, and a description of the same configuration and processing as that of the first embodiment will be omitted. FIG. 12 is a block diagram showing a configuration example of the image display device 400 according to the present embodiment. In FIG. 12, the same functional units as those in FIG. 2 (Example 1) are designated by the same reference numerals as those in FIG. The image display device 400 has an error diffusion processing unit 405 instead of the dither processing unit 105.

The error diffusion processing unit 405 performs conversion processing for each pixel and error diffusion processing for correcting the gradation values of surrounding pixels that have not been converted based on the gradation value error caused by the conversion processing. As a result, the image data OU_DATA is generated from the image data LC_DATA. Then, the error diffusion processing unit 405 outputs the generated image data OU_DATA to the display unit 106. Hereinafter, "peripheral pixels that have not been converted" will be referred to as "unprocessed peripheral pixels". In this embodiment, as the conversion process, a process of converting the number of bits from the number of second bits to the number of first bits is performed by truncating the bits. Then, as the error diffusion process, a process of adding the gradation value corresponding to the bit truncated by the conversion process to the gradation value of the unprocessed peripheral pixel is performed. However, if there are no unprocessed peripheral pixels, the error diffusion processing is omitted. The conversion process is not particularly limited. When the bits are carried forward, in the error diffusion processing, the gradation value corresponding to the bits added for the carry may be subtracted from the unprocessed peripheral pixels.

In this embodiment, the lines to be processed are sequentially switched from the uppermost line of the image to the lowermost line. In the processing of one line, the pixels to be processed are sequentially switched from the leftmost pixel of the line to the rightmost pixel. Then, the pixel adjacent to the right side of the pixel to be processed is used as the unprocessed peripheral pixel. Therefore, in this embodiment, the gradation value corresponding to the bit truncated by the conversion process for the rightmost pixel is deleted without being added to the gradation value of the other pixels. The selection order of the pixels to be processed is not particularly limited. Further, the unprocessed peripheral pixels may be pixels that have not been subjected to conversion processing and exist around the pixels to be processed, and are not limited to pixels adjacent to the right side of the pixels to be processed. .. For example, the unprocessed peripheral pixel may be a pixel adjacent to the lower side of the pixel to be processed.

FIG. 13 is a schematic view showing a specific example of the processing of the error diffusion processing unit 405. FIG. 13 shows the processing corresponding to the pixels I, J, and K. Pixel I is the leftmost pixel, pixel J is the pixel to the right of pixel I, and pixel K is the pixel to the right of pixel J. As shown in FIG. 13, the gradation value of the image data LC_DATA is 3 (12 bits) in all of the pixels I, J, and K.

First, the gradation value 3 (12 bits) of the pixel I is corrected to the gradation value 0 (10 bits) by truncating the lower 2 bits of the gradation value 3 (12 bits) of the pixel I. Then, by adding the lower 2 bits of the gradation value 3 (12 bits) of the pixel I to the gradation value 3 (12 bits) of the pixel J, the gradation value 3 (12 bits) of the pixel J becomes the gradation value. It is corrected to 6 (12 bits).

Next, the gradation value 6 (12 bits) of the pixel J is corrected to the gradation value 1 (10 bits) by truncating the lower 2 bits of the gradation value 6 (12 bits) of the pixel J. Then, by adding the lower 2 bits of the gradation value 6 (12 bits) of the pixel J to the gradation value 3 (12 bits) of the pixel K, the gradation value 3 (12 bits) of the pixel K becomes the gradation value. It is corrected to 5 (12 bits).

Next, the gradation value 5 (12 bits) of the pixel K is corrected to the gradation value 1 (10 bits) by truncating the lower 2 bits of the gradation value 5 (12 bits) of the pixel K. Then, the lower 2 bits of the gradation value 5 (12 bits) of the pixel K are added to the gradation value of the pixel to the right of the pixel K. When the pixel K is the rightmost pixel, the lower two bits of the gradation value 5 (12 bits) of the pixel K are deleted.

Image data OU_DATA is generated by performing the above processing for all pixels. Then, by the above processing, the error of the gradation value due to the conversion processing can be diffused to the surrounding pixels.

As described above, also in this embodiment, the error of the gradation value due to the conversion process can be diffused to the surrounding pixels. As a result, the image data is corrected so that the display corresponding to the specific gradation value is realized by the display element and the display elements around it, and the brightness unevenness of the display image can be reduced with high accuracy. ..

<Other Examples>
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100, 300, 400 Image display device 103: 1st correction unit 104: Bit conversion unit 105, 305: Dither processing unit 107: 2nd correction unit 405: Error diffusion processing unit

Claims (12)

By the display unevenness of the display device by using the first correction value for correcting the input image data of the first number of bits to low reduction, first correction means for generating a first corrected image data of the first number of bits When,
Based on a predetermined first correction value that can be used by the first correction means, the display unevenness is reduced with a higher resolution than that of the first correction means, and a gradation value that cannot be expressed by the first correction image data. The first corrected image data of the first bit number is the first bit number so that the display corresponding to the specific gradation value is realized by the display element of the display device and the display element around the display element. Corrected to the first corrected image data with a larger number of second bits than
In the first corrected image data of the second bit number, the conversion process of converting the number of bits from the second bit number to the first bit number and the error of the gradation value due to the conversion process are added to the surrounding pixels. By applying the error reduction processing to reduce by using
Second correction means for generating the second correction image data and
An image processing device characterized by having. A second correction value that uses a combination of the gradation value of the first correction image data of the first bit number and the predetermined first correction value as an input value and corrects the gradation value, or the floor. Further, it has an acquisition means for acquiring input / output information having a gradation value obtained by correcting the adjustment value using the second correction value as an output value.
The image processing apparatus according to claim 1, wherein the second correction means corrects the first corrected image data having the first bit number based on the input / output information. The display element of the display device includes a thin film transistor which is a driving transistor in a pixel circuit.
The image processing apparatus according to claim 1 or 2, wherein the predetermined first correction value is a first correction value for correcting a gradation value corresponding to a threshold voltage of a thin film transistor as a virtual reference. .. The second correction means corrects the gradation value of a pixel that at least satisfies the condition that the brightness corresponding to the gradation value corresponds to a display element higher than the reference brightness, based on the predetermined first correction value. The image processing apparatus according to any one of claims 1 to 3. The gradation value of the first corrected image data having the first bit number is 0 or more, and is a value obtained by subtracting 1 from the value of the number of gradation values that can be expressed by the first corrected image data having the first bit number . The following integers
In the second correction means, the gradation value of the first correction image data having the first bit number is less than 0.1% of the value of the number of gradation values that can be expressed by the first correction image data. The image processing apparatus according to any one of claims 1 to 4, wherein the gradation value of a pixel satisfying at least the above condition is corrected based on the predetermined first correction value. The second correction means
And facilities the error reduction processing in the first corrected image data of the number of the second bit is a filtering process using a predetermined filter,
The facilities Succoth the conversion processing in the first corrected image data of the second number of bits subjected to the error mitigation processing,
The image processing apparatus according to any one of claims 1 to 5, wherein the second corrected image data is generated. The image processing apparatus according to claim 6 , wherein the second correction means performs a filter process for referring to the plurality of pixels when each of the plurality of pixels satisfies a predetermined condition. The gradation value of the first corrected image data having the first bit number is 0 or more, and is a value obtained by subtracting 1 from the value of the number of gradation values that can be expressed by the first corrected image data having the first bit number . The following integers
The predetermined conditions are
The condition that the brightness corresponding to the gradation value corresponds to the display element higher than the reference brightness, and
The condition that the gradation value of the first corrected image data of the first bit number is less than 0.1% of the value of the number of gradation values that can be expressed by the first corrected image data of the first bit number . When,
7. The image processing apparatus according to claim 7 , further comprising at least one of the above. The second correction means includes the conversion process for each pixel and the error reduction process for correcting the gradation values of surrounding pixels that have not been subjected to the conversion process based on the error of the gradation value caused by the conversion process. The image processing apparatus according to any one of claims 1 to 8, wherein the second corrected image data is generated from the first corrected image data having the second number of bits . The conversion process is a process of converting the number of bits from the second bit number to the first bit number by truncating the bits.
The ninth aspect of the present invention is characterized in that the error reduction process is a process of adding a gradation value corresponding to a bit truncated by the conversion process to a gradation value of a pixel not subjected to the conversion process. Image processing equipment. By the display unevenness of the display device by using the first correction value for correcting the input image data of the first number of bits to low reduction, the first correction step of generating a first corrected image data of the first number of bits When,
Based on a predetermined first correction value that can be used in the first correction step, the display unevenness is reduced with a higher resolution than that of the first correction step, and a gradation value that cannot be expressed by the first correction image data. The first corrected image data of the first bit number is the first bit number so that the display corresponding to the specific gradation value is realized by the display element of the display device and the display element around the display element. Corrected to the first corrected image data with a larger number of second bits than
In the first corrected image data of the second bit number, the conversion process of converting the number of bits from the second bit number to the first bit number and the error of the gradation value due to the conversion process are added to the surrounding pixels. By applying the error reduction processing to reduce by using
The second correction step for generating the second correction image data and
An image processing method characterized by having. A program for causing a computer to execute each step of the image processing method according to claim 11 .

Images